Blasting cap assembly



Dec. 20, 1960 c. F. HORNE ETAL BLASTING CAP ASSEMBLY Filed 001;. 19,1956 FIG.2

'III/II FIG. l2b

FIG. 6

FIG. I34

CHARLES F. HCRNE EDWARD K. LEFREN EDWARDL. RAME JULIUS ROTH INVENTORS BYW W- AGENT United States Patent BLASTIN G CAP ASSEMBLY Charles F. Homeand Edward K. Lefren, Kingston, N.Y., and Edward L. Ramer, Hockessin,and Julius Roth, Wilmington, Del., assignors to Hercules Powder Company,Wilmington, Del., a corporation of Delaware Filed Oct. 19, 1956, Ser.No. 616,964

15 Claims. (Cl. 10228) This invention relates to electric blasting capassemblies and to their manufacture. In one aspect this inventionrelates to the electric blasting cap units which when fully assembledare free from conventional wire bundles and can be safely stored, testedor shipped or otherwise handled independently from the wire bundle, andto their manufacture. In another aspect this invention relates to amulti-step method by which electric blasting caps are manufactured,including the steps of disposing bridged pins in an ignition plug in ablasting cap shell, extending pins from the plug and terminating them inclose proximity to the end of the shell, and subsequent to requisitehandling of the unit thus formed, affixing leg wires to the pins andsealing the juncture with a dielectric material having suitableproperties therefor. In still another aspect this invention relates tothe use of selected dielectric insulating materials for effecting legwire-pin seals in the manufacture of electric blasting caps.

Electric blasting caps, or initiators, are employed for detonating highexplosives. They contain a detonating charge which is fired by passageof electric current through a pair of lead wires, or leg wires, thelatter passed through a plug element in the cap shell and connectedtherein by a resistance or bridge wire which becomes electrically heatedin contact with a heat-sensitive material to cause ignition ordetonation of the said material as the case may be.

Various methods have been employed in the manufacture of electricblasting caps. One such method involves casting a sulfur plug around aset of leg wires, the plug being of size for a snug fit in the capshell; inserting the resulting plug assembly in the shell; pouring amolten asphalt material on the inserted plug of sulfur and around thelead wires extending therethrough, and solidifying same; and thenpouring molten sulfur on the asphalt plug and around the lead wiresabove it, as a topping seal. The leads, as a wire bundle, extend fromthe cap shell. Another method comprises placing the bridged pins in anignition plug and then welding or soldering the lead wires to the pins,at a site away from the live cap, and then inserting the resultingplug-wire assembly into the cap shell to render it ready for use.

Electric blasting caps of the low tension type, i.e., with bridge wireassembly and fired by low voltage current, have heretofore beenassociated with wire bundles attached thereto. This has given rise todifiiculties in respect of storing and handling, particularly in respectof hazards involved as a result of development of static charges on thewire bundles with concomitant accidental firing.

This invention is concerned with electric blasting cap units free fromthe foregoing ditficulties, and with their manufacture, and with theadaptation of such units for use at any time, as desired.

An object of this invention is to provide electric blasting initiators.Another object is to provide for the manufacture of electric blastinginitiators. Another object is to provide electric blasting initiatorsthat can be handled ice as complete units without the usual hazardinherent from development of static charges in the wire bundle, or fromstray currents. Another object :is to provide for the manufacture ofsuch units. Another object is to provide dielectric sealing materialsfor effecting a strong jointure of leg wires with pins of a liveelectric blasting cap under nonhazardous conditions. Other aspects andobjects will be apparent from the accompanying disclosure and theappended claims.

In accordance with this invention a blasting cap is provided whichcomprises a blasting cap shell; a heatsensitive material in said shell;an ignition plug in said shell in waterproof sealed relation with theinterior walls of said shell; electrical conductor pins disposed in saidplug and extending into said shell; a bridge wire conmeeting said pinsin said shell and in operative communication with said heat-sensitivematerial to transfer heat to same, when electrically heated, and saidpins extending upwardly in said plug and terminating in directcommunication with the outside of said shell. Also in accordance withthe invention a blasting cap assembly is provided which comprises ablasting cap shell; a heatsensitive material in said shell; an ignitionplug in said shell in waterproof sealed relation with the interior wallsof said shell; electrical conductor pins disposed in said plug andextending into said shell; a bridge wire conuect ing said pins in saidshell and in operative communication with said heat-sensitive materialto transfer heat to same, when electrically heated, said pin-s extendingupwardly in said plug and terminating in direct communication with theoutside of said shell; a leg wire secured to each pin and a dielectricmaterial sealed around each connected lead wire-pin pair and betweeneach said pair in contact with said cap, said dielectric material beingcapable of effecting a seal with each said leg wire-pin pair to insulateeach said pair of wires from the other and from moisture, and being ofsufficient strength to withstand failure during use of said cap thatwould result in cracking with concomitant leakage of electric currentduring use and breakage of wires.

Further in accordance with this invention is provided a method for themanufacture of an electric blasting cap which comprises disposing in ablasting cap shell a dielectric plug in waterproof sealed relation withthe inner walls thereof and containing electrical conductor pins bridgedin said shell in operative communication with a heat-sensitive materialtherein to transfer heat, when electrically heated, to said material;and extending said pins upwardly in said plug and terminating same indirect communication with the outside of said shell. Still in accordancewith this invention a method is provided for the manufacture of afinished electric blasting cap which comprises disposing in a blastingcap shell a dielectric plug in waterproof sealed relation with the innerwalls thereof and containing electrical conductor pins bridged in saidshell in operative communication with a heat-sensitive material thereinto transfer heat, when electrically heated, to said material; extendingsaid pins upwardly in said plug and terminating same in directcommunication with the outside of said shell; thereafter securing a leadwire outside said shell in electrically conductive contact with eachsaid pin and then sealing a dielectric material around each connectedlead wire-pin pair and between each said pair in contact with said cap,said dielectric material being capable of effecting a seal with eachsaid leg wire-pin pair to insulate each said pair of wires from theother and from moisture, and being of suflicient strength to withstandfailure during use of said cap that would result in cracking withconcomitant leakage of electric current during use, and breakage ofwires.

In a preferred embodiment of our invention a pair of electricalconductor pins is disposed through a dielectric plug of plasticmaterial, e.g., a Bakelite (phenolic resin) plug so that they extendfrom each end of the plug. We prefer to form the plug-pin assembly bymolding the wire around the pins. The pins are connected on one side ofthe plug by a resistance or bridge wire, and the resulting assembly isinserted, bridge wire first, into a cap shell of metal or plasticadapted to receive the plug in tight waterproof sealed relation. Aheat-sensitive material, generally an ignition or delay powder inoperative contact with a base charge to cause detonation of same, isdisposed in the shell below the plug in contact with the bridge wire toreceive heat from the wire when the wire is electrically heated. Thepins are extended upwardly from the plug in the shell and are terminatedat a point in close proximity to the end of the said shell, which asillustrated with reference to the drawings can be inside or outside theshell. The unit thus completed can be tested, stored, shipped orotherwise handled prior to its intended use in the field without therebeing a possible accidental firing as would be the case with such a capwhen connected with a wire bundle. Also, the unit is hermetically sealedand will not deteriorate on storage. Subsequent to such handling and, ifdesired, just prior to actual use, lead wires are secured in physicalcontact with the pins to form respective lead wire-pin pairs, preferablyby mechanical lock, as by a sleeve-type connector. This removes any needfor heat treatment such as during welding or soldering. A plasticdielectric material, capable of maintaining a plastic-Wire moistureproofseal at the point of juncture and of forming a seal with the cap shelland further being of sulficient strength to withstand failure, e.g.,cracks or breakage that would occur during use of the cap, is applied byany suitable method to the wire junctures and cap. Preferably, this isdone by injection molding or thermosetting a resin around the wire pairsand cap. The plastic is disposed between the wire pairs and around them,in contact with the cap shell. The finished cap, including lead wiresconnected to the pins, is in condition for firing under any conditions,including those encountered when exposed to high heads of water in aborehole. It has heretofore been necessary to attach the lead wires tothe pins and seal the joint in the plug at the time of making the cap orextend the lead wires in lieu of pins through the plug to the bridgewire in order to be certain that a waterproof connection of lead wiresto bridge wire would be obtained. That, of course, has made it necessaryto complete the entire cap unit at the time of its manufacture, withinherent hazards during storage and other handling, that have beeneliminated by this invention.

Any dielectric material is a suitable seal material for use in thepractice of this invention that (1) can form a moistureproof seal withthe lead wires and pins at their point of juncture and adjacent baredportions, (2) can adhere to or form a seal with the cap shell andignition plug, (3) is of sulficient strength that it will not crack,break or otherwise mechanically fail during life of the cap, e.g., understorage conditions, shipping and other handling, and actual dispositionand use in the borehole. The seal can be applied by any suitable method,preferably by injection molding or simple molding with a thermosettingresin. We have found polyethylene of softening point of 100 C. andhigher, and thermoplastic ethyl cellulose (at least two ethoxy groupsper anhydroglucose unit) especially adaptable to the injection moldingprocedure. Ordinarily, these seals are formed in a simple split moldmachine, although any suitable mold or injection machine can beemployed.

The seal preferably has about the same base diameter as that of the cap,tapering somewhat toward its end away from the cap shell. Any suitablelength seal can be employed, although a seal extending in the order offrom about A to /2 inch along the wires outside the shell is generallyutilized. Thus, the configuration of the seal is one largely of choice.

The following examples are illustrative of formation of dielectric sealsin accordance with the invention.

Example 1 Thermoplastic ethyl cellulose was injection molded around amechanically locked lead wire-pin jointure of an electric blasting capof this invention. The formulation was, on a weight basis, parts ofethyl cellulose having from about 45.5 to 46.8 ethoxyl groups peranhydroglucose group and having a viscosity of about 70 centipoises asmeasured as a 5 percent solution in 8020 toluene-ethanol at 25 C., about10 parts of Dow Resin V-2 (a trimer of a-methyl styrene), and about 5parts of Santicizer 16 which is butyl phthalyl butyl glycolate. A minoramount of diamyl phenol stabilizer was present.

Example 2 A somewhat softer formulation than that of Example 1 wasemployed in injection molding of a seal around a lead wire-pin jointureof Example 1, namely, parts of ethyl cellulose having from about 45.5 to46.8 ethoxyl groups per anhydroglucose group and a viscosity of about100 centipoises as measured as a 5 percent solution in 8020toluene-ethanol at 25 C., 23 parts of tri-2-ethylhexyl phosphate asplasticizer, and 2 parts diamyl phenol.

Example 3 A seal of clear grade polyethylene of softening point of about212 F. was injection molded around a lead wire-pin jointure and capshell of Example 1.

In each of the three preceding examples the seal was waterproof, ofstrength to withstand failure by cracking, breaking or the like, and wasnot in any way deteriorated at F. storage. The cylinder temperaturesranged from 320-380 F., during the foregoing injection moldings.

In each injection molding procedure a Plasticor molding machine wasemployed. This mold consists of a cavity which grips the lower sectionof the cap shell, the cavity having a constriction to hold the cap shellat the point where it is enlarged by insertion of the ignition plug,generally a molded Bakelite (phenol-formaldehyde) plug. Two narrowcircular holes are provided in the mold to hold the leg wires so thatwhen the cap is placed in the mold, there is a closed cavity between theend of the mold and the upper end of the cap, and it is in this cavitythat the seal material is molded. The mold is provided with guide pinsto maintain its alignment. Obviously, other molding machines and methodscan be employed.

In operation of each of Examples l-3, the mold was readily filled,giving a complete sealed closure of the cap and a well-formed seal,insulating the bare wire pairs from moisture and electric charges.

We have found that thermosetting resins, as well as thermoplasticresins, can advantageously be employed in making the nonconductor sealsof this invention. Thus, any fluid thermosetting resin can be pouredinto a cup mold around the top of the blasting cap and the leg wireleadwire juncture. It is preferred that the cure time of the sealingmaterial be sufiiciently short inasmuch as if it is too long, an undulylarge number of molds are required in a continuous manufacturingprocess. Accordingly, the preferred setting time does not exceed about 5minutes at room temperature, although longer curing times can beemployed, e.g., 30 minutes at 60 C. Curing times may be any suitableduration e.g., up to 45 minutes or longer, although shorter curing timesare obviously most advantageous.

A preferred thermosetting resin material is Stypol 705, astyrene-polyester modified with vinyl toluene to regulate fluidity andcatalyzed with benzoyl peroxide. A promoter is generally employed whenmolding Stypol 705 at room temperature, cobalt naphthenate containingabout 6 percent cobalt being exemplary of a suitable promoter.

Such a system gels, or sets, sufiiciently to be removed from the mold in2-3 minutes at room temperature and becomes completely cured and hard in15 20 minutes at room temperature.

Thermosetting resins of short cure time can be treated in variousmanners to overcome unduly short pot life. Thus, in the above Stypolsystem, the promoter is dissolved in the resin, the latter having a longpot life, and the catalyst is dissolved in a separate resin portion andthe two solutions are mixed just prior to molding. Such mixing can becarried out by way of impinging jets of each solution on the otherdirectly in the mold. Inasmuch as both promoter and catalyst solutionsare stable in themselves at room temperature, no gelation occurs exceptin the mold. Any suitable manner of impinging the separate streams canbe utilized.

When referring herein to cure time, it is meant the time required forcomplete cure or hardening of the resin whereas by set time is meant thetime required for sufiicient gelation or partial cure to take place suchthat the resin can be removed from the mold for completion of cure. Bythe term pot life it is meant the time during which the ingredients arein admixture without set taking place, i.e., prior to the actual step ofmolding.

Cellosolve acetate, ethylene dichloride and acetone are suitablesolvents for the uncured resin system.

The following examples are illustrative of seals of this invention madefrom thermosetting resins.

Example 4 Two solutions of a thermosetting resin were prepared. SolutionA was prepared by mixing, on a weight basis, 80 parts of Stypol 705, 19parts vinyltoluene and 1 part cobalt naphthenate. Solution B wasprepared by dissolving 6 parts of benzoyl peroxide in 20 parts ofstyrene. Twenty-four parts of Solution B were then mixed with 74 partsof Solution A to form Solution C. Solution D was prepared by dissolving2 /2 parts of Naugatuck promoter No. 2 in 97 /2 parts of Solution A.Solutions C and D were then introduced as separate impinging jet streamsinto a cup mold around a leg wire-lead wire juncture and shell top of anelectric blasting cap in equal parts by weight to obtain a seal of thisinvention.

Example 5 A seal was made in accordance with the procedure of Example 4,the final seal composition being 82.5 percent Stypol 107, 1.75 percentbenzoyl peroxide, 0.75 percent Naugatuck promoter No. 2, and 15 percentstyrene. This resin was somewhat less fluid than that of Example 4. Atroom temperature gel time was 3 minutes and hardening time was 15minutes. The resulting cap was immersed in salt water for 6 days at 200p.s.i., the lowest resistance between unbridged leg wires being 30,000ohms and between leg wire and copper shell being 28,000 ohms.

Example 6 Araldite CN504, an ethoxylene-type resin (condensationproducts of polyaryl ethylene oxides with acid anhydrides and amines),was mixed at room temperature with about 15 percent of its weight ofdiethylene triamine. The resulting mixture was poured into a molddisposed around wire junctures and cap shell top as described in Example4. The mixture had appreciable pot life at room temperature and cured inabout 15 minutes at 60 C.

Seals made in accordance with the foregoing Examples 4-6 do not showdeterioration upon hot storage over prolonged periods, and exhibitrequisite physical strength for withstanding failure such as by cracksor breaks and provide requisite electric and moisture insulation for thebared Wire portions. Thus, the seals of Examples 4 and 5 were notadversely affected by several months of hot storage and would not crackat --30 C.

Exemplary of other thermosetting resin seal materials of our inventionare (l) Narmco 3117 (a polyester resin) benzoyl peroxide Naugatuckpromoter No. 2 styrene in respective weight percent proportions of 87.8,1.5, 0.7 and 10, with a gel time of 3 minutes and a hardening time of 15minutes, both at room temperature, (2) Stypol 107E/cyclohexanonehydroperoxide/benzoyl peroxide Naugatuck promoter No. 2/styrene in weight percent respective proportions of 87.2, 0.5, 1.5, 0.8and 10 with a gel time of 4 minutes and a hardening time of 15 minutes,both at room temperature, and (3) Stypol l07E/benzoyl peroxide promoterNo. Z/Lupersol DDM (60 percent solution of methylethylketoneperoxide indimethylphthalate) styrene in respective weight proportions of 87.8,1.0, 0.7, 0.5 and 10, with a gel time of 10 minutes and a hardening timeless than 30 minutes, both at room temperature. Hydroxyheptyl peroxideis also advantageously utilized as the peroxide component.

The invention is further illustrated with reference to the drawings.Fig. 1 is illustrative of a fully assembled unit cap of this invention.Fig. 2 illustrates the unit of Fig. 1 connected with a conventional Wirebundle, such as subsequent to storage and other requisite handling. Fig.3 illustrates a dielectric seal material of this invention and itsapplication to a specially shaped cap to bond the wires and to adhereto, or bond, the shell as the case may be. Fig. 4 illustrates aplastic-type shell disposed around a metal cap shell and which can bedirectly sealed with the leg wires and pins to form a seal of thisinvention. Fig. 5 further illustrates a plastic covered metal shell ofFig. 4, Fig. 6 illustrating strips of sealing material that can beutilized in making the cap of Fig. 5. Fig. 7 shows ears formed, as aresult of employing strips of sealing material heat-sealed to form theplastic shell such as of Figs. 4 and 5. Fig. 8 shows a completed unit inwhich the sealing material comprises a plurality of strips surroundingthe shell and disposed in sealed relationship with the leg wires Whenthe latter are sealed to the cap pins. Fig. 9 illustrates an embodimentemploying use of a sleeve member, metal, plastic or paper, in impartingadditional strength to the seal. Figs. 10 and 11 illustrate anembodiment employing a specific saw-tooth type interlock ing of wiresand pin with termination of the pins inside the shell. Figs. 12a, 12band further illustrate a method for making a blasting cap assembly ofthis invention. Figs. 13a and 13b illustrate a unit cap wherein theignition plug terminates short of the shell end to form a cavity inwhich all or a portion of the dielectric seal can be disposed. Fig. 14illustrates a cavity in the top of the ignition plug in which sealmaterial can be disposed.

With reference to Fig. 1, cap unit 1 constitutes blasting cap shell 2,metal or plastic, containing pins 3 terminating outside shell 2 andbridge wire 4 across pins 3, the bridge wire being in contact with anysuitable heat-sensitive material 5 such as an admixture of mercuryfulminate and potassium chlorate, diazodinitrophenol and potassiumchlorate, nitromannite, lead styphnate, lead azide or the like.Heat-sensitive material 5, although shown as a loose mixture can, ifdesired, be in head, pressed or buttered form. Base change 5a in thebottom and closed end of shell 2 is any suitable material detonatable byheat from ignition of mixture 5 or by detonation of a primer (not shown)disposed intermediate the base charge 5a and ignition mixture 5, anddetonatable by heat from ignition of mixture 5.

Illustrative of suitable base charges are pentaerythritol tetranitrate,tetryl, nitrostarch, cyclonite (cyclotrimethylene trinitramine),mannitol hexanitrate and the like. Illustrative of suitable primercompositions are diazodinitrophenol, lead styphnate, lead azide andmercury fulminate, these compounds also being capable of functioning asignition compounds in the absence of a primer, as is well known in theart.

Ignition plug 6 is disposed in the top and open end of shell 1 andcontains pins 3 extending through it from bridge wire 4 and terminatingin close proximity to the outside of the shell at 7. Ignition plug 6 isassembled in sealed watertight relationship with the interior walls ofshell 2. Ordinarily, a watertight joint is obtained by making theoutside diameter of the plug slightly larger than the inside diameter ofthe shell and pressing the plug into the shell. This causes the shell toexpand or bulge and to frictionally hold the plug in a tight grip.Insertion may be facilitated by slightly tapering the entrance end ofthe plug or by slightly flaring the open end of the shell. A wax layeron the outer plug surface facilitates pressing the plug into the shelland provides an improved watertight fit.

This unit is free from the wire bundle, i.e., leg wires, and can behandled, stored and otherwise moved as desired without the hazardsordinarily present when wire bundles are attached. The unit eliminatesthe undue bulk and weight characteristic of the prior art caps assembledwith leg wire bundle during manufacture, and provides thereby forgreatly simplified handling up to the time of use. Also, the cap unitprovides for a choice of type of lead wires at a time after assembly ofthe cap, such as at the time of use.

Any suitable plug material can be employed. Thermosetting resinmaterials such as rubber, alkyd resins, phenol-formaldehyde resins,urea-formaldehyde resins and sulfonamide resins are examplary. Bakeliteis a now preferred material. Although thermoplastic resins, in someinstances, show a tendency toward cold flow, thermoplastic resins suchas those of polystyrene, vinylidine chloride, cellulose acetatebutyrate, polyamides, vinyl chloride and vinyl acetate have beenemployed. Also, vinyl acetate-vinyl chloride rubber materials, andpolyethylene have proved satisfactory.

Preferably a plug of moldable material is molded around the pins 3, toform the plug-pin assembly. Thus, either a stiff or soft pin can beemployed. However, if desired, the pins, if sufiiciently stiff, can beinserted in and through the plug by hand or by mechanical means.Exemplary pin materials are iron, steel, copper, nickel, nickel-silver,silver and Invar.

The initiator shell 2 is either metal or plastic. By way of example, itmay be made from any desirable copper alloy, aluminum, bronze or similarductile metalilc material or from any suitable plastic material such asthermosetting molding compositions based on resins of thephenol-formaldehyde, casein-formaldehyde, ureaformaldehyde, andphenol-furfural types, and thermoplastic molding compositions formulatedfrom cellulose esters, cellulose ethers, polymerized esters of acrylicand substituted acrylic acids, polystyrene, chlorinated rubber, modifiedisomerized rubber, vinyl chloride, vinyl acetate polyethylene and thelike.

Fig. 2 illustrated the wire bundle 8, i.e., insulated lead wires 9 withbared portions 9a connected with bare pins 3 at 7a. Attachment at thispoint is preferably by mechanical locking, e.g., by a crimped sleeveconnector; it being an advantageous feature of this invention that heattreatment of any kind need not be employed in connecting the leg wiresand pins. Although soldering can be employed with quite some degree ofsafety, we prefer to effect jointure by mechanical locking to assuremaximum safety. However, welding or soldering can be utilized ifdesired.

With reference to the embodiment of Fig. 3, a plastic seal material 11of this invention surrounds the bared portions of wire bundle 8 and pins3 connected at 711., making a bond to the bared wires and also to theshell 2. A true bond between the sealing material 11 and the cap shelland/ or ignition plug is not essential, provided there will be noseparation or failure at such points. Shell 2 as at 12 and 12a isparticularly advantageously employed without such a bond of shell andseal material. Thus, the top or neck portion 12a of Fig. 3 extends intothe seal body 11 in a manner to lend support to the body 11 in lieu ofsupport recived from a true bond. However, we prefer a true bond betweenseal material and cap and/or ignition plug in order to assure againstall current leakages even though small leakages can be tolerated.

When the cap shell 2 is of material similar in heatsealing properties tothe sealing material, then the materials may be made to blend togetherand provide a true seal so that the bared Wires and pins, the sealmaterial and the shell form a unitary mass. This can be done withoutadversely affecting the cap itself in any manner, and provides for addedstrength of the dielectric seal 11.

With reference to Fig. 4, an open end shell 11a of plastice sealmaterial of this invention is molded so as to accept a unit cap (Fig. 1)with pins 3 terminating in the open end 12 of the shell, and so thatinsulated wire portions 9 when attached at 7a to pins 3 will also bewithin the open end 12. As illustrated with reference to Fig. 5, theopen end 12 is then pressed down under pressure, and heat is locallyapplied to cause the bared wires and shell to form a seal of thisinvention. This seal, when desired, can function as a waterproof sealfor the entire cap unit. It is advantageous in accordance with thisembodiment to add an extra portion of sealing material between the leadwire-pin pairs prior to making the final seal so as to provide addedprotection against shorting across the lead-pin junctures inside theplastic shell.

Figs. 6 and 7 illustrate another embodiment involving an over-allplastic coating of the metallic shell and the Wire junctures. A strip11b of thermoplastic seal material of this invention is formed on eachside of the metal shell as one illustrated with reference to Fig. 7. Thefinal structure is shown with reference to Fig. 8 in which the twostrips 11b are sealed along the lines 14 all around the edge of themetallic cap 2, forming a point structure at 16 and a seal of Fig. 5around the insulated wires 9, thereby covering all points of the metalshell unit including the projecting pins and the bared lead wires. Theears at 14 which are formed by the closing together of the strips ofmaterial as illustrated in Fig. 7 may be sheared off.

The plastic covering illustrated (11a, Figs. 4, 5 and 11b, Figs. 6, 7,8) provides corrosion protection for the metallic shell 2 and throughits insulating property also provides protection against stray currents.The plastic covering of this embodiment can be of appropriate warningcolor such as bright red, orange, yellow, white, etc., and can also bestamped or marked with such words as Explosives Dangerous or any othersuch warnings.

The embodiments of Figs. 4-8 provide a still further advantage, namely,that molding of the plastic seal material around the entire finishedassembly is eliminated and only such seams as seams 14 of Fig. 7 need beheated. Although such an overall molding operation can be carried out,it is inadvisable inasmuch as the heat content of the plastic coveringmaterial can be of sufiicient magnitude, during molding, that heat-flowinto the cap 2 from the plastic tube during molding might cause theexplosive inside the shell to reach temperatures that are not adequatelysafe. In accordance with the embodiments of Figs. 4-8, the amount ofheat required for closing the thermoplastic envelope is a minimum andwill under no circumstances cause development of unsafe temperatures inthe explosive.

In another embodiment, Fig. 9, the bared leg wires 3 extending from capshell 2 and terminating at 7a are connected with the bared lead wires 9aof bundle 8 and then a supporting sleeve 10, such as of metal, plasticor paper, is formed on the cap end encompassing the bared wire portionsand extending to the covered lead wire 9. Seal material is then pouredor injected into the form in contact with the shell and insulated leadwire to form the solid plastic seal. The sleeve can lend additionalsupport to the seal dependent upon the seal material selected which willbe particularly advantageous in that the seal material can be selectedfrom a broader strength range of materials. The sleeve 10 permitssetting up of a seal over longer periods than otherwise consideredpracticable for forming the seal from a thermosetting resin. The sleevein effect serves as an expendable unit mold.

With reference to Figs. 10 and 11 is shown an additional embodiment ofmechanical locking that can be employed in the practice of ourinvention. Thus,pins 3 are sawtoothed and are terminated within cavity6a of plug 6 in the cap shell so as to accept bared leads 9a of wirebundle 8, also saw-toothed, in locked relationship all within the upperportion 6a of plug 6. A thermoset plastic seal material of thisinvention is then poured into the cavity portion 6a to cure and setaround the wire-pin connection 7a and an insulated wire portion 9. Thisembodiment, as that of Fig. 9, provides for a selection from a broaderstrength range of seal materials, inasmuch as the seal materialsupported by the plug cavity can be gelled away from the moldingoperation and a longer gelling time becomes more practicable. It isadvantageous in this embodiment to select a resin that will cure and setat about 150 C. or lower, preferably at about room temperature, such asthe composition of Example 5. However, if cooling is employed, highercuring temperatures can be employed. The seal material is advantageouslyextended to above the shell to impart added strength to the overallseal, and in that event the saw-toothed portions can be in the plug orabove it, as desired. However, to the extent that there is no sleevesupport for the extended seal material, set times somewhat shorter thanthose employed with the sleeve will be more practicable from themanufacturing standpoint. Fig. 11 illustrates the plastic seal andsaw-toothed connection in place.

With reference to Figs. 12a, 12b and 120 is further illustrated our nowpreferred method embodiment. A cap shell 2 formed from any suitablematerial such as above described, generally a copper alloy, is formedwith closed end 22 and open end 21 and charged with a base charge a anda heat-sensitive material 5. A dielectric plug 6, generally a phenolicresin material, is molded around pins 3, and bridge wire 4 is welded orsoldered across pins 3 as shown in Fig. 12b. The plug assembly of Fig.12b is then wax-coated and inserted into the open shell end 21 to form atight waterproof fit with the inner wall of shell 2. The distance fromplug 6 to bridge wire 4 is such that when the resulting plug assembly isinserted, bridge wire first, in cap 2, the bridge wire when heated willbe in operative contact with the heat-sensitive material 5 to transferheat to it to cause ignition of same. Pins 3 of unit 25 are extendedfrom plug 6 to a point 7a in close proximity to the outside of shell 2.That can be done by terminating the extended pins either before or afterinsertion of unit 25 in shell 2.

Insulated leg wires 9 of wire bundle are bared at 9a and mechanicallylocked with pins 3 at 7a, such as by a crimped sleeve connector to formseparate legwire-pin pairs a and 1; connecting with bridge wire 4.

A plastic seal material 26 of this invention, ethyl cellulose andpolyethylene being now preferred materials, is then injection molded, aswith a Plasticor machine described hereinabove, around and between eachleg wirepin pair a and b and in contact with cap shell 2 and insulatedwires 9, to form a leg wire-pin shell seal of this invention.

It is understood that all dielectric seals of this invention encompassthe bare pins and bared leg wire portions and a portion of the leg wireinsulation and, in most instances, a portion of the cap. shell. In thoseinstances wherein the dielectric seals do not contact the shell, theydirectly contact the plug 6. All seals are moisture resistant andexhibit the characteristics set forth herein. When referring herein totermination of pin wires in direct communication with the outside of thecap shell, it is meant that there is no intervening agency between theterminated pin ends and the outside of the shell so that leg wiresoutside the shell can always be directly connected with the pins as 10by soldering or by mechanical lock as with a locking sleeve connector.Thus, whether the pins are terminated inside or outside the plug, theyare always in direct communication with the outside of thecap shell andcan be directly connected with leg wires.

The. pins are terminated at points within the shell or outside asillustrated. However, in any event, they do not extend outside the shellbeyond points in close proximity to the shell end. Such distance, aswill be appreciated, is variable dependent upon the size of each cap pinand leg wire and the manner in which the leg wires are to be connectedwith the pins. By way of example, a suitable connection of pin with legwire can generally be made in any event when pins extend above theshell, say from Va to 2 inches. However, in some instances, it may bedesirable to extend the pins a somewhat greater distance, such as whenemploying a plastic outer shell as illustrated with reference to Figs. 4and 5.

With reference to Figs. 13a and 13b, a unit cap such as of Fig. 1contains ignition plug 6 terminated short of the top shell end so thatafter the shell end is crimped, there will be a cavity formed into whichthe dielectric seal material can be inserted. Although the seal materialin the cavity is sufiicient in the practice of this invention when theleg wire-pin jointures and insulated wire portions 9 are in the cavity,it can in any event form a part of an overall body of seal materialextending above the shell end along the leg wires as shown withreference to Fig. 13b to provide a locking action on the seal above theshell to further strengthen the over-all seal.

Although generally the seal material will be placed in direct contactwith the metal or plastic shell wall, it can if desired be disposed incontact with the ignition plug only. Thus, in some instances, the plugmay extend outside the shell and the seal disposed in direct contactwith the plug material and out of contact with the shell. Preferably,the ignition plug is placed about flush with the shell top end and thepins extend as stubs a short distance above or away from the plug. Uponconnecting the leg wires and pins, the dielectric seal material, in mostinstances a plastic material, can be applied and contacted with the capshell. However, as above discussed, the seal material can be contactedwith the plug only, if desired.

As illustrated with reference to Figure 14 a cavity 6b in plug 6 can beprovided for accepting additional seal material in support of the legwire-pin seal. Cavity 6b can be utilized with or Without the additionalcavity of Figure 1 (also shown in Figure 13a) intermediate plug 6 andthe top end of shell 2.

When referring herein to bridge wire structure conmeeting or bridgingconductor pins inside the cap, it is meant to include ignitionassemblies wherein the bridge wire bridges the pins through conductorsextended from the pins, e.g., bridge wires in a matchhead assemblyconnected with the pins to conductors extended from the ends of thepins.

As will be evident to those skilled in the art, various modificationscan be made or followed in light of the foregoing disclosure anddiscussion without departing from the spirit or scope of the disclosureor from the scope of the claims.

What we claim and desire to protect by Letters Patent 1s:

1. In an electric blasting cap assembly comprising an elongated shellclosed at one end and open at the other end, and having water imperviouswalls, an ignition plug within said shell in transverse water-tightclosing relation therewith, a heat-sensitive composition in said shellbetween said ignition plug and said closed end; a pair of conductorwires extending into said shell through the said open end and throughsaid ignition plug, and a bridge wire connected across the terminatingends of said conductor wires in operative communication with saidheat-sensitive composition to cause actuation of same by transfer ofheat upon passage of electric current through said conductors and saidbridge wire, the improvement comprising said ignition plug disposedwithin said shell intermediate the said shell ends to divide said shellinto an enclosed portion and an open end cavity portion; said shellbeing crimped at its open end to form a lip directed inwardly toward theshell axis, said conductor wires extending from said bridge wire throughsaid plug and said cavity to the outside of said shell and terminatingadjacent the said open shell end and lip; a separate lead wire outsidesaid shell secured to each said conductor wire at the end thereofterminated as above described; a plastic dielectric material, as aunitary mass, filling said cavity and abutted therein against the shellwell, said ignition plug, and the inner wall of said lip, and extendingfrom said cavity around and between each connected pair oflead-conductor wires in sealed relationship with each said connectedpair of lead-conductor wires and the walls of said shell and said lip toinsulate each said pair from each other and from moisture.

2. An assembly of claim 1 wherein a cavity is also disposed in the topend of said ignition plug and a portion of said dielectric material isplaced in the last said cavity.

3. A blasting cap assembly of claim 1 wherein said dielectric materialis ethyl cellulose.

4. A blasting cap assembly of claim 1 wherein said dielectric materialis a polyethylene having a softening point about 100 C.

5. A blasting cap assembly of claim 1 wherein said dielectric materialis a styrene polyester.

6. A blasting cap assembly of claim 1 wherein said dielectric materialis an ethoxylene-type resin.

7. In the manufacture of an electric blasting cap wherein a dielectricplug containing conductor wires extending therethrough is sealed withinan elongated cap shell containing an open end and a closed end intransverse water-tight closed relationship therewith, and wherein saidconductor wires are bridged within said shell in operative relationshipwith a heat-sensitive material to transfer heat to said material whenelectrically heated, and wherein said conductor wires are extended fromtheir bridged ends through said plug to the outside of said shell asufficient distance for connecting with an electric power source remotefrom said shell, the improvement comprising forming an assemblycomprising said ignition plug with said conductors extendingtherethrough and connected on one side of said plug with a bridge wire,and terminating the ends of said conductors opposite said bridged endsto extend from said plug as described hereinafter; inserting theresulting ignition plug assembly, bridge wire first, through the openend of said shell into said shell and in said transverse water-tightclosing relationship therewith, a distance sufficient to divide saidshell into an enclosed portion containing said bridge wire and an openend cavity portion and to extend the said terminated ends of saidconductors through said cavity and said open shell end to the outside ofsaid shell adjacent the said open end; crimping the said open end ofsaid shell to form an inwardly extending lip toward the shell axis;connecting a separate lead wire outside said shell with each conductorwire at its end terminated as above described; and then sealing eachsaid pair of connected wires from each other and from moisture byfilling the said cavity with a plastic dielectric material, as a unitarymass, so as to abut said material against said ignition plug and theinner walls of said shell and lip and then extending said mass from saidcavity around and between each said connected pair of conductor-leadWires to insulate each said pair from the other and from moisture.

8. A blasting cap assembly comprising an elongated blasting cap shellhaving an open end and a closed end; a heat-sensitive material in saidshell; an ignition plug in said shell in water-proof sealed relationwith the posed in, and extending through, said shell; a bridge wireconnecting said pins in said shell and in operative communication withsaid heat-sensitive material to transfer heat to same when electricallyheated, said shell being crimped at its open end to form a lip directedinwardly toward the shell axis and said ignition plug abutting theresulting lipped inner shell wall, about its periphery, to retain theopening in said crimped end as an open cavity; said pins extendingupwardly through said plug and terminating at a point in close proximityto the crimped end of said shell; a separate lead wire secured to eachpin, and a plastic dielectric material sealed around each connected pairof lead-pin wires and between each said pair and extended into saidcavity against said plug to insulate each said pair from the other andfrom moisture.

9. An assembly of claim 8 wherein each said pin extends from saidignition plug to a point outside said shell.

10. An assembly of claim 8 wherein said pins are terminated inside acentrally disposed cavity in the top end of said plug and aresaw-toothed, wherein said lead wires are saw-toothed to engage said pinsin said centrally disposed cavity, and wherein said plastic material isdisposed in said centrally disposed cavity.

11. An assembly of claim 8 wherein the said pin wires extend throughsaid plug to a point outside said shell, wherein a supporting sleeve isadapted to connect with said cap shell and encompass said lead wire-pinpairs at their point of juncture and wherein at least a portion of saiddielectric material is disposed in said sleeve.

12. In an electric blasting cap assembly comprising an elongated shellclosed at one end and open at the other end, an ignition plug withinsaid shell in transverse watertight closing relation therewith, aheat-sensitive composition in said shell between said ignition plug andsaid closed end; a pair of conductor Wires extending into said shellthrough the said open end and through said ignition plug, and a bridgewire connected across the terminating ends of said conductor wire inoperative communication with said heat-sensitive composition to causeactuation of same by transfer of heat upon passage of electric currentthrough said conductors and said bridge wire, the improvement comprisingsaid ignition plug disposed within said shell intermediate the saidshell ends to divide said shell into an enclosed portion and an open endcavity portion; said shell being crimped at its open end to form a lipdirected inwardly toward the shell axis, said conductor wires extendingfrom said bridge wire through said ignition plug into and through atleast a portion of said cavity to a point in close proximity to thelipped open end of said shell; a separate lead wire outside said shellsecured to each said conductor wire at the end thereof terminated asabove described; a plastic dielectric material, as a unitary mass,filling said cavity and abutted therein against the shell wall, saidignition plug, and the inner wall of said lip, and extending from saidcavity around and between each connected pair of lead-conductor wires insealed relationship with each said connected pair of lead-conductorwires and the inner wall of the lipped end of said shell to insulateeach said pair from each other and from moisture.

13. In the manufacture of an electric blasting cap wherein a dielectricplug containing conductor wires extending therethrough is sealed withinan elongated cap shell containing an open end and a closed end intransverse water-tight closed relationship therewith, and wherein saidconductor wires are bridged within said shell in operative relationshipwith a heat-sensitive material to transfer heat to said material whenelectrically heated, and wherein said conductor wires are extended fromtheir bridged ends through said plug toward the outside of interiorwalls of said shell; electrical conductor pins dissaid shell asufiicient distance for connecting with an electric power source remotefrom said shell, the improvement comprising forming an assemblycomprising said dielectric plug with said conductor wires extendingtherethrough and connected on one side of said dielectric plug with abridge wire, and terminating the ends of said conductor wires oppositesaid bridged ends to extend from said ignition plug as describedhereinafter; inserting the resulting assembly, bridge wire first, intosaid shell through the said open end thereof into said transversewater-tight closing relationship therewith, a distance sufficient todivide said shell into a closed end portion containing said bridge wireand an open end cavity portion and to extend the terminated end of eachsaid conductor wire through at least a portion of said open end cavityto a point in close proximity to the open end of said shell; crimpingthe said open end of said shell to form an inwardly extending lip towardthe shell axis; connecting a separate lead wire, from outside saidshell, with each conductor wire at the end thereof in close proximity tosaid open shell end as described; and then sealing each said pair ofconnected wires from each other and from moisture by filling the saidcavity with a plastic dielectric material, as a unitary mass, so as toabut said material against said dielectric plug and the inner walls ofsaid cavity and then extending said mass from said cavity around andbetween each said connected pair of conductor-lead wires to insulateeach said pair from the other and from moisture.

14. In a process of claim 13, forming said assembly by injection moldinga dielectric plug around a pair of the said conductor wires and thenconnecting each said conductor wire with said bridge wire as described.

15. In a process of claim 13, inserting said plug assembly in said shella distance such that when said shell is crimped, as described, theresulting lip can be pressed down upon said plug to retain an openingthrough the resulting crimped end as said cavity, and then so crimpingthe said shell open end onto said plug.

References Cited in the file of this patent UNITED STATES PATENTS 1UNITED STATES PATENT OFFICE CERTIFICATION OF CORRECTION Patent No.2,965,033

December 20, 1960 Charles F. Horne et al.

It is hereby certified that error appears in the above numbered patentrequiring correction and that the said Letters Patent should read ascorrected below.

Column 6, charge exemplary read 4-- plastic read above about 100 C.

line 58, for "Base change" read Base column '7, line 25, for "exemplary"read lines 42 and 43, for "metalilc" read metallic line 52 for"illustrated" read M illustrates for "reclved" read received line 74,

column 8, line 12, for "plastics"; column 11, line 28, for "about 100C."

Signed and sealed this 9th day of May 1961,

(SEAL) Attestz- ERNEST W, SWIDER Attesting Officer DAVID L, LADDCommissioner of Patents UNITED STATES PATENT OFFICE CERTIFICATION OFCORRECTION Patent No; 2,965,033 December 20 1960 Charles F, Horne et al.

It is hereby certified that error appears in the above numbered patentrequiring correction and that the said Letters Patent should read ascorrected below.

Column 6 line 58, for "Base change" read Base charge column 7,, line 25for '"examplary" read exemplary lines 42 and 43, for "metalilc" readmetallic line 52, for "illustrated" read illustrates line 74, for"recived" read received column 8 line 12 for plastic read plastic column11, line 28, for "about 100 C." read above about 100 C.

Signed and sealed this 9th day of May 1961.

(SEAL) Attestz- ERNEST W, -SWIDER DAVID L. LADD Attesting OfficerCommissioner of Patents UNITED STATES PATENT OFFICE CERTIFICATION OFCORRECTION Patent No; 2965 033 December 20 1960 Charles F. Home et a1.

It is hereby certified that error appears in the above numbered patentrequiring correction and that the said Letters Patent should read ascorrected below.

Column 6 line 58 for "Base change" read Base charge column 7, line 25for ""examplary" read exemplary lines 42 and 43, for "metalilc" readmetallic line 52 for illustrated" read illustrates line 74, for"recived" read received column 8 line 12, for "plastic read plasticcolumn ll line 28 for "about 100 C." read above about 100 C.

Signed and sealed this 9th day of May 1961 (SEAL) Attest:

ERNEST W, -SWIDER DAVID L-o LADD Attesting Officer Commissioner ofPatents

